1. Field of the Invention
The present invention relates to a backlight assembly and a liquid crystal display device having the same, and more particularly, to a backlight assembly with uniform brightness and a liquid crystal display device having the same.
2. Description of the Related Art
Recently, liquid crystal display (LCD) devices have become smaller and lighter with more powerful performance. While the widely used cathode ray tube (CRT) technology has advantages in performance and price, CRTs have disadvantages in slimness and portability.
In contrast, LCD technology has advantages such as slim profile, light weight and low power consumption, thereby solving the disadvantages of CRT technology. As a result, LCDs are widely used in almost all information processing devices using a display.
Backlight assemblies used for light sources in LCDs can be classified into an edge type backlight assemblies and direct type backlight assemblies according to their cylindrical lamp arrangement. An edge type backlight assembly has a lamp unit installed on the side of a light guide panel for guiding light. The lamp unit includes a lamp to emit light, lamp holders inserted on both sides of the lamp to protect the lamp, and a lamp reflection plate. The lamp reflection plate covers circumferential surface of the lamp with its side inserted on the side of the light guide panel to reflect light from the lamp to the light guide panel.
Accordingly, the edge type backlight assembly having the lamp unit installed on the side(s) of the light guide panel is usually applied to relatively small-sized LCDs, such as monitors of laptop or desktop computers. The edge type backlight assembly has good light uniformity, high durability, and slim profile.
Meanwhile, the direct type backlight assembly has been developed typically for 20-inch LCD displays or larger. Here, a plurality of lamps is aligned on the bottom of a diffusion plate to directly illuminate light on a front side of an LCD panel. The direct type backlight assembly is widely used for a large-sized LCD displays that require high brightness because light utilization of a direct type backlight assembly is higher than that of an edge type backlight assembly.
FIG. 1 is an exploded perspective view of a related art direct type backlight assembly LCD. As shown in FIG. 1, a related art direct type LCD includes a liquid crystal panel 105 and a backlight assembly. The liquid crystal panel 105 includes a bottom substrate with a plurality of pixels arranged in a matrix form, a top substrate with R, G, B color filter layers and a black matrix, and a liquid crystal layer interposed between the top and bottom substrates. The backlight assembly provides light to the liquid crystal panel 105.
The backlight assembly includes a plurality of lamps 113 for emitting light toward the bottom of the liquid crystal panel 105, a lamp holder 111 for fixing the plurality of lamps 113 with a predetermined distance, optical sheets 107, a diffusion plate 108 disposed between the liquid crystal panel 105 and the lamps 113, support frames 110a and 110b for fixing the optical sheets 107 and the diffusion plate 108 at both sides, and a reflection plate 117 disposed on the bottom of the lamps 113. Two lamps 113 form a pair, and each respective pair of lamps 113 is fixed by a lamp guide 109 with a predetermined distance. Additionally, the reflection plate 117 is attached to the inside of a bottom cover 120.
That is, the liquid crystal panel 105, the optical sheet 107, the diffusion plate 108, the support frames 110A and 110B, the lamps 113, and the reflection plate 117 are stacked in the bottom cover 120. Thereafter, a top case 101 is mounted to protect the stacked parts. An inverter 123 for supplying a voltage is mounted on a rear side of the bottom cover 120, and an inverter cover shield 124 is mounted on the inverter 123. A cover shield 121 prevents static electricity.
FIG. 2 is a partial perspective view of the lamps 113 fixed by the lamp guide 109 according to a related art. As shown in FIG. 2, the lamps 113 are mounted on the inside of a bottom cover. The lamps 113 are fixed by a lamp guide 109 in pairs. The lamp guide 109 includes a guide plate 109a and two lamp fixing parts 109b, and each pair of the lamps is respectively fixed by the lamp part 109b. The lamp guide 109 is mounted on the reflection plate 117 in a line and plays a role in holding the lamps when an external impact or vibration is applied.
FIG. 3 is a plan view of a related art lamp guide 109. As shown in FIG. 3, the lamp guide 109 includes the guide plate 109a and the lamp fixing part 109b, and the lamp fixing part 109b is disposed on both edges of the guide plate 109a. More specifically, the lamp fixing part 109b is vertically disposed on a central axis of the guide plate 109a. In the structure of the lamp guide 109, brightness deterioration in a region of the lamp guide 109 does not occur due to characteristics of light such as diffusion, reflection, refraction, and diffraction if there is an enough distance between the lamp and the diffusion plate.
However, as the LCD becomes small-sized, light weight and slim in profile, brightness deterioration occurs in a region of the lamp guide 109 due to a close distance between the lamp and the diffusion plate. Specifically, since brightness deterioration severely occurs in the region of the lamp fixing part 109b, a black line defect appears along with the lamp guide 109. Therefore, the picture quality is deteriorated characterized by a non-uniform brightness over the liquid crystal panel.